The objective of the program is to recognize allergy-proneness at the earliest feasible age. Amniotic fluid, maternal and cord blood samples have been taken at or close to the delivery time of children from families with and without historiesof hypersensitivity. Follow-up histories and samples are being taken. Radioimmunoassay methods for measuring serum IgE, IgD, and IgG4 levels have been developed. Measurements are being made and correlated. Preliminary results suggest that amniotic fluid IgE and IgD levels are determined in general by fetal factors and not directly by maternal blood levels. Reciprocal relationships between IgD and IgE antibodies have been observed in allergic children and children with pulmonary hemosiderosis over a period of time. Evidence for raised levels of IgE in acute infections with EBV and CMV has been found.